An electrooptical apparatus will be set up to measure the diffraction pattern of a laser beam shining through a thin uniform cardiac muscle. Previous investigators have shown that the zero to first order spacing has a defined (ksin-1) relation to sarcomere spacing in that region. This apparatus will be used to extend our previous phenomenological modelling of cardiac muscle from the macroscopic to the sarcomere level. Both twitching muscles and muscles in drug induced contractures will be investigated. We will also try to put electrolytically sharpened 75u pins into the belly of cat papillary muscle. By detecting the distance between the pins by an electrooptical system, one can measure the length of a segment of undamaged muscle. We will then analyze the muscle mechanical properties in vitro using a linear servo-motor and microprocessor controller. A step response method will be used and the results correlated to previous work in which the muscle length was measured including the damaged ends.